### Theory:

When performing operations with monomials as fractions, the mathematical transformations are the same as in common fractions.
Example:
Add the monomials $\frac{5{x}^{2}y}{4}+\frac{7{x}^{2}y}{4}$
1) Add the expressions in the numerators.

2) If possible, reduce the numeric factors of the numerator and the denominator.

Example:
Subtract the monomials $\frac{{a}^{4}{b}^{2}}{8}-\frac{2{a}^{4}{b}^{2}}{3}$
1) Make denominators the same.

2) Subtract the expressions in the numerators.

This fraction cannot be simplified.
Example:
Multiply the monomials $\frac{7{m}^{3}}{2}\cdot \frac{\mathit{mn}}{5}$
1) When multiplying the fractions, multiply the numerators and multiply the denominators.

2) Multiply the variables by adding their exponents. Remember: if the exponent of a variable factor is not specified, then it is $$1$$.